The invention relates generally to a method and apparatus for identifying a cylinder undergoing a compression stroke in an internal combustion engine. More particularly, the invention pertains to a method and apparatus for rapidly identifying a compression cylinder of an internal combustion engine during startup of the engine, in order to establish a proper ignition timing sequence.
The following background information is provided to assist the reader to understand the invention described and claimed herein. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically so indicated.
A cylinder of a typical internal combustion engine undergoes four different sequential strokes during a single complete cycle of the engine: an intake stroke, a compression stroke, a combustion (or xe2x80x9cpowerxe2x80x9d) stroke, and an exhaust stroke. The spark plug of a particular cylinder is typically fired/actuated at some point near the end of the compression stroke (e.g., at a certain number of degrees before top dead center of the compression stroke is reached). This is typically termed the amount by which the spark is xe2x80x9cadvancedxe2x80x9d, and allows for a certain amount of lag time required for the combusting fuel to spread and therefore supply sufficient power to the particular piston. The combustion stroke then follows, in which the piston is forcibly moved toward the crankshaft by the expanding combusting gas. During these four strokes, there are two strokes in which the piston of each cylinder is moving in a direction away from the crankshaft: the compression stroke and the exhaust stroke.
During an initial startup, where the internal combustion engine is being powered by a typically electrically powered motor (e.g., a xe2x80x9cstarter motorxe2x80x9d powered by the battery of the vehicle), it is important to identify which pistons of the internal combustion engine are undergoing the compression stroke, so that the correct spark plug wire (or xe2x80x9charnessxe2x80x9d wire) may be energized by the ignition coil so as to fire the appropriate spark plug at the top (or near top dead center, minus advancement) of the cylinder(s) which are undergoing a compression stroke.
Earlier internal combustion engines did not require that the particular cylinder (or cylinders) undergoing a compression stroke be identified during the startup process, since mechanical linkages between a xe2x80x9cdistributorxe2x80x9d (e.g., via a xe2x80x9crotorxe2x80x9d) and the camshaft always assured that a spark would be applied to the correct cylinder(s) (e.g., those undergoing a compression stroke).
More modern internal combustion engines have eliminated the distributor and rotor arrangement, and thus correct identification of the cylinder(s) undergoing a compression stroke during startup is a necessity, in order that a correct timing sequence of firing the cylinders can be established.
Various methods and apparatuses have been utilized and proposed in order to correctly and efficiently identify compression cylinders during the startup procedure of an internal combustion engine and thus initialize a correct timing sequence.
A camshaft sensor has been used for compression cylinder identification. Since the camshaft controls the opening and closing of the intake and exhaust ports for the various cylinders, the rotational positioning of the camshaft uniquely identifies which cylinders are undergoing a compression stroke and allows for correct initiation of the firing sequence.
Thus, in such schemes, the camshaft position sensor""s signal is used by engine control module (typically a microprocessor) to fire the desired cylinder. Such camshaft rotational positioning sensors can prove expensive, however, both in materials cost and in the cost of installation. Moreover, failure of such a part during the life of the engine, can give rise to a costly repair.
Another example of compression cylinder identification is described in U.S. patent application Ser. No. 09/972,824, entitled xe2x80x9cMethod of Identifying Engine Cylinder Combustion Sequence Based on Combustion Qualityxe2x80x9d and filed on Oct. 5, 200 which relates to a so-called xe2x80x9cIon Sensexe2x80x9d system of cylinder identification. Here, the spark plugs of all cylinders are actually fired during the startup procedure. At the same time, the spark plugs are used as sensors for measuring the ionization occurring at subsequent cylinders during the actual combusting of the fuel/air mixture during startup. From this ionization feedback, it is possible to determine which of the various cylinders are actually undergoing compression, and thus initiate a proper firing sequence of the spark plugs. Once the cylinder identification is accomplished, the firing continues in the sequential mode, and the xe2x80x9cIon Sensexe2x80x9d system thereafter monitors combustion quality, detecting irregularities like misfires and engine knock.
The California Air Resources Board (or xe2x80x9cCARBxe2x80x9d) is requiring misfire detection with no delay at start beginning with the year 2001. xe2x80x9cStartxe2x80x9d is defined under this standard as the engine reaching within 150 RPM of the hot stabilized idle RPM. For a currently employed xe2x80x9cIon Sensexe2x80x9d algorithm, for room temperature starts, the delay is  less than 0.5 sec. Therefore, the CARB requirement is not met for the first 0.5 sec.
Accordingly, one objective of the invention is the provision of a method and apparatus for rapidly identifying a cylinder undergoing compression in an internal combustion engine in order to initiate a correct ignition timing sequence.
Another objective is the provision of a method and apparatus for compression cylinder identification that does not require costly sensors for detecting the angular positioning of either the camshaft or the crankshaft of the engine.
A still further objective of the invention is the provision of a method and apparatus for precombustion cylinder identification wherein it is not necessary to either actually fire the spark plugs of the engine or to supply a fuel/air mixture to the cylinders of the engine during the period of time before the correct timing sequence of the engine is acquired. This is in contrast to the above-described xe2x80x9cIon Sensexe2x80x9d method of timing sequence acquisition. In the present invention, the cylinder identification takes place either substantially instantaneously or requires, at most, one full engine cycle (i.e., two crankshaft revolutions). During such time, a fuel/air mixture need not be supplied to the cylinders. That is, during cylinder identification according to the present invention, there is no actual combustion of fuel and firing of the spark plugs is unnecessary.
Yet another object of the invention is the provision of a method and apparatus for cylinder identification which is inexpensively implemented and repaired, and which is reliable in operation.
In addition to the objectives and advantages listed above, various other objectives and advantages of the invention will become more readily apparent to persons skilled in the relevant art from a reading of the detailed description section of this document. The other objectives and advantages will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein.
The foregoing objectives and advantages are attained by the various embodiments of the invention summarized below.
In one aspect, the invention generally features a method for identifying a time during which a cylinder of an internal combustion engine is undergoing a compression stroke. The method includes the following steps: An electrode gap is provided and is disposed within the cylinder of the internal combustion engine. A power supply is provided, and the electrode gap is supplied with a voltage differential from the power supply through a circuit. The internal combustion engine is cranked, and the voltage differential across said electrode gap is monitored to determine whether pulses are present in the voltage differential across the electrode gap during such time when the electrode gap is being supplied with the voltage differential and internal combustion engine is being cranked. Preferably, a spark plug, which would normally be installed in the cylinder, furnishes the electrode gap.
In another aspect, the invention generally features an apparatus for identifying a time during which a cylinder of an internal combustion engine is undergoing a compression stroke. The apparatus includes an electrode gap disposed substantially within the cylinder of the internal combustion engine, a power supply, a circuit supplying the electrode gap with a voltage differential from the power supply, and a monitoring circuit for monitoring the voltage differential across the electrode gap to determine whether pulses are present in the voltage differential across the electrode gap during a time when the electrode gap is being supplied with the voltage differential from the power supply and the internal combustion engine is being cranked. Preferably, a spark plug, which would normally be installed in the cylinder, furnishes the electrode gap.